1. Field of the Invention
This invention relates to a mounting structure of a speaker to be mounted on a vehicle (hereinafter referred to as “speaker for vehicle”) for performing acoustic reproduction in a passenger room.
2. Description of the Related Art
As seen from FIG. 4, conventionally, a vehicle 1 such as a passenger car has various speakers for car audio. Generally, since a passenger in a room 2 such as a driver of the vehicle 1 listens to left-right two-channel stereophonic reproduction in a posture facing forward of the vehicle 1, speakers 3, 4 and 5 are mounted at left and right positions in spaces in an instrument panel 6, left and right front doors 7 and 8, and a trunk room 9. Particularly, since the passenger(s) who listens to an acoustic output takes a posture facing forward of the vehicle 1, in many cases, the speaker for vehicles 3 and 4 are arranged in the instrument panel 6 on the front side of the passenger room 2 or the doors 7 and 8 on the side thereof. Since these portions do not have so large a usable space, there is a case in which bass speakers 5 are separately mounted in a space of a rear trunk room of the vehicle in a manner that they are opened in an upper rear tray. Since the directionality of an acoustic output is not so conspicuous at a low frequency, stereophonic feeling is not deteriorated so much in monophonic reproduction based on left and right synthesis in a bass range.
As a conventional mounting structure of a speaker for vehicle, FIG. 5A shows a structure in which the speaker for vehicle 4 shown in FIG. 4 is mounted in the door 7, and FIG. 5B shows a structure in which the speaker for vehicle 3 shown in FIG. 4 is mounted in the instrument panel 6. As seen from FIG. 5A, in many cases, a speaker unit 10 is attached to the door 7, and a space defined between an interior member 11 and a side plate 12 at the outermost position of a vehicle body serves as a speaker box. This space is provided to accommodate a door glass 13 when opening a window by lowering the door glass. The speaker unit 10 thus attached must not interfere the door glass 13. The speaker unit 10 has a flange 15 on the outer periphery of a frame 14. The flange 15 is secured to the periphery of an opening made in the interior member 11 by a bolt 16 and nut 17. As seen from FIG. 5B, the speaker 3 attached to the instrument panel 6 has a speaker unit 10 accommodated in a speaker box 18. A mount fitting 19 is secured by a bolt 16 and nut 17.
Regarding speakers attached for performing acoustic reproduction in a vehicle, JP-A-5-276588 discloses a prior art for arranging a bass range reproduction device in an armrest provided in a passenger room of a passenger car. JP-A-11-54963 discloses a prior art which uses a buffer material so as to cover the peripheral edge of an attaching hole when an electronic instrument to be mounted on a vehicle is attached to the attaching hole. Further, JP-A-5-187422 discloses a prior art applying a buffer material to a screw grommet used for fixing a spare tire in a trunk room of the vehicle. JP-A-5-56830 discloses a prior art of covering a speaker for performing an acoustic reproduction for a man sitting on a seat with a foaming elastic material serving as a core of a chair cover used for a sitting chair.
Such the speaker for vehicle must perform comfortable acoustic reproduction in a passenger room. For comfortable acoustic reproduction, it is required not only the sound quality in a frequency characteristic of the reproduced sound but also the transient sound quality to be good. When the acoustic output is reproduced from the speaker, the transient sound quality of the reproduced sound is deteriorated if the sound is also reproduced from the other portion than a diaphragm of the speaker. The sound is reproduced from the other portion than the diaphragm of the speaker when the frame of the speaker unit or an electric acoustic conversion portion such as a magnetic circuit vibrates, and the speaker box vibrates by the transmitted vibration owing to the counter force generated when the diaphragm of the speaker emits the acoustic output into the air.
If the speaker is covered with the foaming elastic material such as a chair cover as disclosed in JP-A-5-56830, it is expected that the unnecessary acoustic emission from the other portion than the diaphragm of the speaker is prevented. However, in this prior art, since the speaker is embedded in the chair cover to be mounted in the sitting chair, the speaker must be arranged for each seat when applying this prior art to the passenger room 2 of the vehicle 1 as shown in FIG. 4.